1. Field of the Invention
The present invention relates to an electric rotating machine and, more particularly, to an electric rotating machine including a stator to which concentrated winding is applied.
2. Description of the Related Art
Conventionally, in stators of a three-phase induction motor, distributed winding has been applied. On the other hand, in permanent magnet-type motors, stators to which concentrated winding is applied are often employed. A large difference between a concentrated winding stator and a distributed winding stator is that in the concentrated winding stator, there is a negative-phase magnetic flux (running in a direction opposite to a rotational direction) in frequency close to fundamental wave in a magnetomotive force waveform. This fact results in disadvantages such as occurrence of pulsation (ripple) or worse power factor, in an induction motor of such a type as carrying a current on the secondary side by a magnetic flux that the stator generates and producing a magnetic flux. However, concentrated winding stators have merits mainly from the viewpoint of productivity such as high mass production, small coil end, and high space factor.
Under the background as describe above, concentrated winding in stators of an induction motor has been taken into consideration. For example, the following technique is disclosed. In this related art, a stator consists of a plurality of stators axially divided; one divided stator is located being displaced only by an angle β circumferentially with respect to the other divided stator; and a coil of stator winding is wound individually on each teeth of the divided stators, so that the above-described negative-phase magnetic flux may be eliminated (see, for example, the Japanese Patent Publication (unexamined) No. 298578/1995 (e.g., claim 1)).
Nevertheless, in the technique disclosed in the Japanese Patent Publication (unexamined) No. 298578/1995, a coil end will be needed even at the axially central portion. Thus, one of the advantages of small coil end incidental to the concentrated winding is lost. Moreover, depending upon configuration, there are some cases of larger coil end than that of distributed winding type. That is, advantage of the concentrated winding type cannot always be exhibited. This problem remarkably comes out particularly in motors of a small stack thickness.